Hydraulic cushion mechanism

ABSTRACT

A hydraulic cushion mechanism embodying a piston adapted to receive an impact moving within a bore wherein a decreasing clearance between the cylinder and bore is provided, the piston being equipped with an accumulator to maintain separation between air and oil.

United States Patent 1191 Stembridge Mar. 26, 1974 [54] 3,653,301 4/1972 Clendenim et a] 1. 267/119 X [76] Inventor: Harold E. Stembridge, 600 E.

Greenwood Ave., Mt. Prospect, III. P r Examiner-"Robert p 60056 v Attorney, Agent, or Firm-Dawson, Tilton, Fallon & 22 Filed: 0a. 16, 1972 Lungmus 21 A 1. N0.: 297 591 1 pp 57 ABSTRACT 52 us. c1 267/130, 267/34 267/119 A hydraulic cushicm mechanism embodying a Piston 51 1111. C1 51617/00 adapted receive an impact moving Within bme [58] Field of Search 267/34 119 130 wherein a decreasing clearance between the cylinder and bore is provided, the piston being equipped with 5 References Cited an accumulator to maintain separation between air UNITED STATES PATENTS and 3,488,045 H1970 Balunas, Jr. et a]. 267/119 2 Claims, 2 Drawing Figures 1 HYDRAULIC CUSHION MECHANISM BACKGROUND AND SUMMARY OF INVENTION The inventive hydraulic cushion provides protection for an infinite variety of uses such as automatic meat slicers, packaging equipment, automatic bottling machines, plastic forming equipment, etc. where impact can cause serious damage to or destruction of manual and automated equipment. This avoids downtime, repair, replacement and loss of productionnAlthough cushioning devices have been available to the prior art there has been lacking a relatively miniaturized, rugged, inexpensive and totally contained hydraulic cushion that can absorb from 50 to 9,000 inch pounds and without undesirable spring back.

According to the invention, a piston having a projecting stern which receives the impact is housed within a hydraulic cylinder and whereinthe clearance between the piston and the cylinder bore decreases according to an exponential pattern to maintain a constant or relatively constant pressure behind the piston with the changing factor of a decreasing velocity. Further, the rod is equipped with an accumulator mechanism which prevents oil and air contact or mixing so as to insure repetitive performance.

The invention is described in conjunction with an illustrative embodiment, in which FIG. 1 is a prespective view of the exterior of the hy-' draulic cushion mechanism; and

FIG. 2 is a diametral section of the device of FIG. 1.

In the illustration given, and with reference to FIG. 1, the numeral designates generally the body of the cushion which is cylindrical in nature and can be advantageously equipped with external threads 11. Alternatively, a rear stud (not shown) can be provided for convenient mounting. Projecting from the forward end of the body 10 is a stem 12 provided with a forward end 13 which is adapted to receive and cushion an impact. Seen in the center of the circular end surface 13 is a bore or vent 14 which permits the egress of air upon impact and ingress of air when the mechanism is returning to ready condition.

Referring now to FIG. 2, it will be seen that the inner end of the stem 12 is equipped with a piston 15. The piston 15 is advantageously secured to the inner end of the stem 12 by means of a plurality of pins 16 which are fixed at their inner ends within a steel reenforcing ring 17.

It will be noted that the piston 15 is equipped with a flared integral skirt portion 18 which provides a recess or socket for the receipt of the stem 12. The outer surface of the skirt portion 18 is tapered in proceeding rearwardly (considering the front of the mechanism to be the impact surface 13). Advantageously, the taper is of the order of about 2.

The body 10 is equipped with an interior opening 19 so as to accommodate the piston 15. At its forward end, the opening 19 is closed by the stem bearing 20. At its rear end, the opening 19 is constricted as at 21 to provide an enclosure and seat for a piston return spring 22. The return spring 22 extends between the end wall 10a of the body 10 and a constricted portion 23 on the rear end of the piston 15. The rear wall 10a is equipped with a plug closed aperture 24 which permits filling the mechanism with hydraulic fluid.

The rod bearing 20 is held in place by means of radially inwardly extending pins 25 and the bearing 20 is suitably grooved for the receipt of a seal 26 for the stem 12. The rod bearing 20 is also recessed for the receipt of a further seal 27, it being appreciated that the seal 26 is a dynamic seal in that it operates in conjunction with the moving stem 12 whereas the seal 27 is the static seal operating to close any clearance between two non-moving parts, i.e., the rod bearing 20 and the body 10. The forward end of the rod bearing 20 is equipped with a rod wiper 28 to prevent outside contamination from entering the interior of the body 19, the rod wiper 28 being held in place by means of a wiper housing 29 which is press-fitted on the rod bearing 20.

The rod or stem 12 is seen to be of hollow construction with the hollow interior being designated 30. It is with the hollow interior 30 that the vent opening 14 communicates. Slidably mounted within the opening 30 is an accumulator piston 31 urged rearwardly by means of an accumulator or spring 32. The accumulator piston 31 is equipped with a suitable seal as at 33 preventing leakage of hydraulic fluid from one side of the piston 31 to the other. On the rear side of the piston 31, the hollow stem or rod 12 is equipped with a plurality of radially extending passages 34 which permit fluid flow therethrough. Further, the piston 15 (more particularly the constricted rear end portion 23) is equipped with an axial bore 35 which receives a ball check valve 36. The check valve 36 is held against movement out of the bore 35 in a rearward direction by means of a pin 37 while the forward end of the bore 35 is constricted and thereby provides a valve seat.

OPERATION As a moving object comes into contact with the front face 13 of the rod 12, the force of the kinetic energy pushes the rod 12 and rod piston 15 toward the rear of the cylinder body 10. This action compresses the piston return spring 22 and puts pressure on the oil contained in the space 38, thereby forcing the oil to seek an escape route. The path taken is through an ever decreasing orifice slot. This orifice slot is the decreasing clearance between the inner diameter of the opening 19 and the outside diameter of the piston 15, especially the skirt portion 18. The decreasing clearance is designed in a manner to maintain a constant or relatively constant pressure behind the piston with the changing factor of a decreasing velocity. For this purpose, the opening 19 or what in effect is the cylinder bore is produced with a plurality of diameters. The major portion in proceeding from the forward end of the opening 19 has a constant bore or diameter. Thereafter I provide a section of the length of the opening 19 with a slight taper as at 19a which may be of the order of W taper. Finally, the last portion is equipped with a further taper as at 1% of the order of about 2. During the rearward movement of the piston 15, the principal pressure drop occurs between the very forward end of the integral skirt portion 18 and the inside diameter of the opening 19. This persists until the piston is virtually moved all the way rearwardly, i.e., until the clearance between the rear end of the piston 15 and the bore 1% is smaller than that at the forward end of the piston whereupon the location of the pressure drop transfers and effectively halts further rearward movement.

During the initial rearward movement of the piston 15, the hydraulic fluid moves toward the front of the cylinder, i.e., into the space 39 which exists between the rear of the rod bearing 20 and the front end of the piston 15, more particularly, the extreme forward end of the integral skirt portion 18. As displacement of the hydraulic fluid occurs, oil flows into the clearance between the inner diameter of the piston and the outer diameter of the rod 12 and through the radially extending passages 34. These passages, it will be appreciated, also extend through the retaining ring 17. Oil ultimately comes into the interior of the stem or rod 12 and on the rear side of the accumulator piston 31. As oil is forced into the inside of the rod, it pushes the accumulator piston 31 forwardly and compresses the accumulator spring 32. Air contained in the area 30 is forced out of the air vent 14. Meanwhile, the ball 36 blocks passage of oil from the space 38 to the space 40 the latter being on the rearward side of the accumulator piston 31.

As soon as the inward or rearward movement of the piston 15 stops, the ball 36 is moved off of the seat provided at 41 by the bore 35 and allows oil to return from the area 40 to the area 38. As soon as the load is removed from the rod 12, both the piston return spring 22 and the accumulator spring 32 extend to normal size. As the accumulator spring 32 expands, it pushes the accumulator piston 15 toward the rear of the rod 12. This forces the oil out of the rod and draws air into the head of the rod through the air vent 14. During all of this time, the oil and air are kept separate. As the piston return spring 22 extends, it pushes the rod piston 15 and rod 12 toward the front of the cylinder body 10. Oil from the area 40 returns to the area 38 through the holes 34 in the rod 12 and retaining ring 17, through the area between the outer diameter of the rod and the inner diameter of the piston, around the face of the piston and then between the outer diameter of the piston and the inner diameter of the cylinder to the area 38. Some oil also returns lhrough the check valve arrangement at 35 and 36.

The bore or opening 19 provided in the cylinder-like body 10 has, in effect, an exponential pattern of taper. Even though I have referred to changing clearances, it will be appreciated that these are relatively small. For example, with a piston having a 7% inch diameter the maximum clearance is of the order of 0.008 inch while with a larger diameter piston, viz., of the order of 1% inches, the maximum clearance is of the order of 0.050 inch.

I claim:

1. A hydraulic cushion mechanism comprising a body providing a piston-receiving opening, a piston having a rod projecting from said opening and sealed therein, hydraulic fluid within said opening, said opening and piston being contoured to provide an exponentially decreasing clearance, said rod being hollow and having an accumulator piston mounted therein, spring means in said hollow rod for urging said accumulator piston toward the first mentioned piston, spring means in said opening urging said first mentioned piston so as to extend said rod, and port means in said rod between said first mentioned piston and said accumulator piston to permit displacement of hydraulic fluid from said opening into said hollow rod.

2. The structure of claim 1 in which said first mentioned piston is equipped with check valve means for limiting flow from said opening into said hollow rod upon an impact force being applied to said rod but wiich permits flow from said hollow rod to said opening upon release of said impact force. 

1. A hydraulic cushion mechanism comprising a body providing a piston-receiving opening, a piston having a rod projecting from said opening and sealed therein, hydraulic fluid within said opening, said opening and piston being contoured to provide an exponentially decreasing clearance, said rod being hollow and having an accumulator piston mounted therein, spring means in said hollow rod for urging said accumulator piston toward the first mentioned piston, spring means in said opening urging said first mentioned piston so as to extend said rod, and port means in said rod between said first mentioned piston and said accumulator piston to permit displacement of hydraulic fluid from said opening into said hollow rod.
 2. The structure of claim 1 in which said first mentioned piston is equipped with check valve means for limiting flow from said opening into said hollow rod upon an impact force being applied to said rod but wiich permits flow from said hollow rod to said opening upon release of said impact force. 